Important things while changing rcon password/ Rcon setup Instructions
1. Make sure that new Rcon password has more than 8 characters else it might not work
2. Do not set rcon password at server.cfg. If there is any line set rcon_password at the server.cfg file, then put a "//" before that to avoid loading that line
3. Always set rcon password at startup command line.
ie When you stop server there will be a field to enter your rcon password before starting the server.
4. Also, make sure control password is same as rcon password.
ie. You need to also set your new rcon password as control password at Server Control page -> Edit > control password
5. Make Sure to set rcon password fields for associated services.
For Example B3: Since B3 uses rcon to communicate with your server, it needs your new rcon password in order to connect to the server. So Edit rcon password setting of B3 at B3control page-> Edit -> Go to custom fields -> Rcon password